Surface-enhanced Raman scattering (SERS) has successfully been used for a variety of analytical applications. Herein, I examine previous application of the technique to analytical sciences, then continue to discuss my contribution to the field. This begins with the development of glutathione functionalized silver nanoparticles for trace detection of uranium in the form of the uranyl ion. A ratio of the area of the uranyl ion symmetric stretch mode to a glutathione reference band is dependent on uranyl concentration, giving a limit of detection of 24 ppb, which is below the EPA safe drinking limit of 30 ppb. The system is shown to be effective in the presence of interferences and in ground water by simply treating the sample with nitric acid. Our method is additionally shown to be transferrable to a portable hand-held Raman spectrometer, showing it is capable of field use.
Further studies on uranyl detection are carried out using surface-enhanced hyper-Raman scattering as the analytical method. An interesting change in selection rules is observed in the SEHRS spectrum of 4-mercaptobenzoic acid upon addition of uranyl nitrate solution. The change in the spectrum is much more pronounced in the SEHRS data than in the SERS data, suggesting counterintuitively that SEHRS, a nonlinear technique, might be more sensitive than its linear analog. Additional study leads to the result that 4-MBA functionalized particles analyzed by SEHRS yield a limit of detection of 90 ppb, the first trace detection achieved using SEHRS.
Previous SERS studies have almost exclusively relied on the functionalization of surfaces with thiol or amine containing molecules, as these groups have proven affinity for SERS-active surfaces. Unfortunately these groups have shown instability in select environments, alternative functionality is therefore, necessary. The latter portion of this dissertation discusses progress made in alternative functional groups for surface modification. Gold SERS-active surfaces were functionalized with N-heterocyclic carbenes (NHCs) allowing the first measurement of SERS spectra of a NHC. Further experiments determine that the NHC-functionalized films are stable in a variety of environments, giving hope for measurement of SERS data from environments with extreme pH and temperature, and different solvent conditions. A reversible reaction was demonstrated on the surface, suggesting promise for post synthetic modification of surfaces. The NHC-surface system demonstrates comparable, and in some cases superior, stability to thiol-metal surfaces, giving the first viable alternative to thiol functionality for SERS experiments.
Theoretical treatment of both imidazolium and benzimidazolium NHC systems determine that the carbenes withdraw a gold atom from the surface in a pseudo-tip fashion in order for the N-isopropyl groups to be in the most favored position. This effect suggests that the R groups have a profound effect on the measured SERS spectra. Agreement between experimental and theoretical spectra allow for the assignment of bands and also detail an important shift in energy of ring modes upon binding of the carbene to the surface.
|School:||University of Notre Dame|
|Department:||Chemistry and Biochemistry|
|School Location:||United States -- Indiana|
|Source:||DAI-B 80/06(E), Dissertation Abstracts International|
|Keywords:||N-heterocyclic carbene, Raman scattering, Sers, Uranyl|
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